line3d = function(from_position, to_position)
--from https://github.com/ryanramage/bresenham3d/blob/master/index.js
--lua port by jin_xi
   local line = {}
   local temp

   local x0 = math.floor(from_position.x)
   local y0 = math.floor(from_position.y)
   local z0 = math.floor(from_position.z)
   local x1 = math.floor(to_position.x)
   local y1 = math.floor(to_position.y)
   local z1 = math.floor(to_position.z)

   --'steep' xy Line, make longest delta x plane
   local swap_xy = math.abs(y1 - y0) > math.abs(x1 - x0)
   if swap_xy then
      temp = x0; x0 = y0; y0 = temp --swap(x0, y0);
      temp = x1; x1 = y1; y1 = temp --swap(x1, y1);
   end
   
   local swap_xz = math.abs(z1 - z0) > math.abs(x1 - x0)
   if swap_xz then
      temp = x0; x0 = z0; z0 = temp --swap(x0, z0);
      temp = x1; x1 = z1; z1 = temp --swap(x1, z1);
   end
   
   --delta is Length in each plane
   local delta_x = math.abs(x1 - x0)
   local delta_y = math.abs(y1 - y0)
   local delta_z = math.abs(z1 - z0)
   
   --drift controls when to step in 'shallow' planes
   --starting value keeps Line centred
   local drift_xy = (delta_x / 2)
   local drift_xz = (delta_x / 2)
   
   --direction of line
   local step_x = 1
   if x0 > x1 then step_x = -1 end
   local step_y = 1
   if y0 > y1 then step_y = -1 end
   local step_z = 1
   if z0 > z1 then step_z = -1 end
   
   --starting point
   local y = y0
   local z = z0
   
   --step through longest delta (which we have swapped to x)
   local cx, cy, cz
   for x = x0, x1, step_x do
      
      --copy position
      cx = x; cy = y; cz = z
      
      --unswap (in reverse)
      if swap_xz then
	 temp = cx; cx = cz; cz = temp --swap(cx, cz)
      end
      if swap_xy then
	 temp = cx; cx = cy; cy = temp --swap(cx, cy)
      end
      
      table.insert(line, { x = cx, y = cy, z = cz } )

      --update progress in other planes
      drift_xy = drift_xy - delta_y
      drift_xz = drift_xz - delta_z
      
      --step in y plane
      if drift_xy < 0 then
	 y = y + step_y
	 drift_xy = drift_xy + delta_x
      end
      
      --same in z
      if (drift_xz < 0) then
	 z = z + step_z
	 drift_xz = drift_xz + delta_x
      end
   end
   return line
end